The Influence of Green Coffee Bean Extract Supplementation on Blood Glucose Levels: A Systematic Review and Dose-Response Meta-Analysis of Randomized Controlled Trials

Abstract

Studies regarding the influence of green coffee extract (GCE) on blood glucose levels are conflicting. Thus, we sought to conduct a meta-analysis and systematic review of all available randomized controlled trials (RCTs) to quantify the effects of GCE and CGA intervention on blood glucose and insulin levels. We performed systematic online searches in Scopus, Web of science, and PubMed databases, from inception to July 2019. Data were combined analyzed using a random effects model (Der Simonian-Laird method) and reported as weighted mean differences (WMD). Ten trials reported the influences of GCE on FBS and insulin and were subsequently entered into the meta-analysis. Combined results highlighted that FBS was significantly altered after GCE consumption (WMD: -1.791 mg/dl, 95% CI -3.404, -0.177), with no significant heterogeneity among the studies (I-2= 35.0%,p= .128). However, overall results demonstrated that GCE administration did not result in any significant alteration in insulin levels (WMD: -0.925 mu U/ml, 95% CI:-1.915, 0.064), with significant heterogeneity found across studies (I-2= 87.9%). In sub-group analysis, insulin levels were significantly reduced when GCE was supplemented in dosages of >= 400 mg/day (WMD:-1.942 mg/dl, 95% CI:-1.184, -0.975;I-2= 0.0%). The results of present study support the use of GCE for the enhancement of blood glucose, while subgroup analysis highlighted significant improvements in insulin levels when GCE is supplemented in doses >= 400 mg/day.